The class of drugs exhibiting opium or morphine-like properties is referred to as opioids, or opioid agonists. Certain opioids act as agonists, interacting with stereo specific and saturable binding sites in the brain and other tissues. Endogenous opioid-like peptides are present in areas of the central nervous system that are presumed to be related to the perception of pain; to movement, mood and behavior, and to the regulation of neuroendocrinological functions. Three classical opioid receptor types, mu (μ), delta (δ), and kappa (κ), have been studied extensively. Each of these receptors has a unique anatomical distribution in the brain, spinal cord, and the periphery. Most of the clinically used opioids are relatively selective for μ receptors, reflecting their similarity to morphine. However, it is important to note that opioid containing drugs that are relatively selective at standard doses will often interact with additional receptor subtypes when given at sufficiently high doses, leading to possible changes in their pharmacological effect. This is especially true as opioid doses are escalated to overcome tolerance.
The potential for the development of tolerance, physical and/or psychological, dependence (i.e., addiction) with repeated opioid use is a characteristic feature of most opioid containing drugs. The possibility of developing addiction is one of the major concerns in the use of opioids for the management of pain. Another major concern associated with the use of opioids is the diversion of these drugs from a patient in legitimate pain to other individuals (non-patients) for recreational purposes.
Drug abusers and/or addicts typically may take a dosage form containing one or more opioid analgesics and crush, shear, grind, chew, dissolve and/or heat, extract or otherwise damage the product so that a significant amount or even an entire amount of the drug becomes available for immediate absorption by 1) injection, 2) inhalation, and/or 3) oral consumption.
There are three basic patterns of behavior leading to opioid abuse. The first involves individuals whose opioid drug use begins in the context of medical treatment and who obtain their initial drug supplies through prescriptions from physicians. The second begins with experimental or “recreational” drug use and progresses to more intensive use. A third pattern of abuse involves users who begin in one or another of the preceding ways but later switch to oral opioids such as methadone, obtained from organized addiction treatment programs.
There are various routes of administration an abuser may commonly attempt to abuse an opioid containing drug formulation. The most common methods include 1) parenteral (e.g. intravenous injection), 2) intranasal (e.g., snorting), and 3) repeated oral ingestion of excessive quantities of orally administered tablets or capsules. One mode of abuse of oral solid drugs involves the extraction of the opioid component from the dosage form by first mixing the dosage form with a suitable solvent (e.g., water), and then subsequently extracting the opioid component from the mixture for use in a solution suitable for intravenous injection of the opioid to achieve a “high.”
Attempts have been made to diminish abuse of orally administered opioid drugs. These attempts generally centered on the inclusion in the oral dosage form of an opioid antagonist which is not orally active but which will substantially block the analgesic effects of the opioid if one attempts to dissolve the opioid and administer it parenterally.
For example, commercially available Talwin®Nx tablets from Sanofi-Winthrop contain a combination of pentazocine and naloxone. Pentazocine is a partial agonist of μ receptors and also has affinity for κ receptors, whereas, naloxone is an antagonist of μ receptors. Talwin®Nx contains pentazocine hydrochloride equivalent to 50 mg base and naloxone hydrochloride equivalent to 0.5 mg base. Talwin®Nx is indicated for the relief of moderate to severe pain. The amount of naloxone present in this combination has no action when taken orally, and will not interfere with the pharmacologic action of pentazocine. However, this amount of naloxone given by injection has profound antagonistic action to opioid analgesics. Thus, the inclusion of naloxone is intended to curb a form of misuse of oral pentazocine, which occurs when the dosage form is solubilized and injected. Therefore, this dosage has lower potential for parenteral misuse than previous oral pentazocine formulations.
U.S. Pat. No. 6,559,159 (Carroll et al.) describes the use of kappa receptors antagonist for the treatment of opioid related addictions. One such compound is naltrexone, which is commercially available in the tablet form Revia® for the treatment of alcohol dependence and for the blockade of exogenously administered opioids. (Physicians Desk Reference 57th ed., Montvale, N.J.)
U.S. Pat. No. 6,375,957 (Kaiko et al.) describes in detail the combination of opioid agonist, NSAID, and an orally active opioid antagonist. The purpose of adding the opioid antagonist is the same as discussed above.
U.S. Pat. No. 4,457,933 (Gordon et al.) describes in detail a method for decreasing both the oral and parenteral abuse potential of analgesic agents such as oxycodone, propoxyphene and pentazocine by combining an analgesic dose of the analgesic agents with naloxone in specific, relatively narrow ranges.
U.S. Pat. No. 6,228,863 B1 (Palermo et al.) describes a method for reducing the abuse potential of an oral dosage form of an opioid analgesic, whereby an orally active opioid agonist is combined with an opioid antagonist into an oral dosage form requiring at least a two-step extraction process to be separated from the opioid agonist, the amount of opioid antagonist included being sufficient to counteract opioid effects if extracted together with the opioid agonist and administered parenterally.
The prior art describes several other methods and compositions to minimize the abuse of an opioid containing drug. One such method is discussed in U.S. Pat. No. 6,593,367 (Dewey et al.), describing a method whereby the addiction-related behavior of a mammal suffering from addiction could be changed by a combination of drugs. The method includes administering to the mammal an effective amount of gamma vinyl GABA (GVG) or a pharmaceutically acceptable salt, or an enantiomer or a racemic mixture, where the effective amount is sufficient to diminish, inhibit or eliminate behavior associated with craving or use of the combination of abused drugs.
U.S. Pat. Nos. 4,175,119 and 4,459,278 (Porter et al.) describe compositions and methods useful for the prevention of accidental and/or intentional oral overdoses of a drug.
In summary, various attempts have been made and are described in prior art to develop abuse-deterrent dosage forms. Clearly there is a need for a delivery system for commonly used oral dosage formulations (e.g., immediate release, sustained or extended release and delayed release) of drugs, and in particular analgesics such as opioid analgesics, for patients seeking drug therapy and which deters abuse and minimizes or reduces the potential for physical or psychological dependency.